I just realized that during the course of the show, the OP has changed from episode to episode, so that no spoilers were revealed; new characters appeared, or turn around, or were shaded out near the beginning, and near the end they were fully visible.

It's a nice unique way of doing the OP, and I wish more shows would do something similar. I've seen too many spoiler-ridden OPs (especially on longer running series), so this is a breath of fresh air.